CIPD and other HR organisations
The first resource is Google and these may refer you to places such as the CIPD or other human resources organisations with which many HR professionals are affiliated. They may have some resourceful guides that can help you navigate situations using the "generalities". Usually these are very brief steps that you should take advising on the best practice for the course of actions and the sequences needed for you to operate within employment law and lets you know what your employees' rights are.
HR specialists are usually the best resource because they are able to provide you with specific advice that is tailored to your situation. Whilst some of these specialist are expensive on an hourly basis, many companies such as HR Dept have many affordable options such as monthly payment plans that scale as the size of your business does. Another valuable and often hidden benefit is the HR insurance that is offered that may cover your business for tribunal costs and other employment related legal expenses to varying levels depending on the extent of the insurance that is purchased.
Searching on Bark or PeoplePerHour
Another useful resource may be search engines for professionals such as Bark.com or PeoplePerHour.com. There are also other professional services organisations that may have searchable lists so you can find the best professional to suit your HR needs.